Extrusion molding of plastic wire
DATE：2022/10/20 8:27:14 / READ： / SOURCE：This station
Extrusion molding of plastic wire
① The single screw extruder with the screw diameter of 45mm or 65mm is generally selected for the extrusion of PE monofilament. The length diameter ratio L/D of the screw is ≥ 20:1, the compression ratio is (3.5~4): 1, and the thread is of isometric sudden change type or isometric gradual change type.② The mold structure for PE monofilament extrusion molding is mostly rectangular, as shown in Figure 9-2.
Figure 9-2 Structure of Right angle Monofilament Molding Mold
Conical hole D at molten material inlet of mould: d~
1-Perforated plate; 2 One barrel mold transition cone;
3-mold specific; 4 - Connecting flange; (2~4): 1, the diversion cone angle is about 50 °,
5-Shunt cone; 6 - spinneret; Add three layers of 40/80/40 mesh filter screen in front of the orifice plate.
7 - Fastening screws; 8 - Temperature measuring hole forming die The plate of forming wire strip is spinneret
Figure 9-3 shows an enlarged view of the spinneret of part 6 in the mold. This part shall be made of alloy steel with high temperature resistance, small deformation and strong wear resistance. After finishing, heat treatment is also required to improve the hardness and wear resistance of the working face with the hole diameter.
In the figure, the commonly used hole diameters for forming thread on spinneret plate are 08mm, 0.9mm and
1.0mm, the ratio of the hole length to the diameter is (4~10): 1, and the taper angle at the feeding end is 20 °. After finishing the spinneret, it is required that the diameter of the forming wire shall be consistent, the distance between the center lines of each hole shall be equal, and the inner surface of the hole diameter shall be smooth and flat without scratches, burrs, and stagnation.
③ Cooling water tank The function of the cooling water tank is to cool and shape the molten material extruded from the mold with formed wires. The cooling water tank is formed by welding and combination of steel plates, with guide rollers running inside. The structure is shown in Figure 9-4. The tank body is 1~2m long and 1m high. The cooling water temperature in the tank is adjustable within the range of 20 °~40 °, and the distance between the cooling water level and the die spinneret is adjustable within the range of 20~50mm. Component composition. The function is to reheat the cooled and shaped preform and stretch it, so that its molecular chains are rearranged into an ordered structure consistent with the length direction, so as to improve the working strength of the finished silk. The drawing method is to heat the wire blank to a temperature lower than its melting temperature (no more than 150 ℃), and then draw the wire blank to the required specification of the finished product depending on the speed difference between the front and rear drawing rolls.
The heating method for drawing monofilament can be the circulation heating of hot air in the oven or the heating of the preform with 100 ℃ boiling water. The stretching ratio can be up to 10 times. The length of heating water tank shall not exceed 3m generally.
⑤ Pressure lead screw The pressure lead screw is a group of smooth and flat steel rolls with chromium coating on the surface, which are respectively installed at the inlet and outlet of the stretching heating water tank. The pressure screw entering the water tank pressurizes the drawing screw blanks, which is conducive to the drawing and arrangement of the screw blanks; The pressure lead screw at the outlet tank end is actually a rotating guide roller, and the pressure lead screw at the front and back of the water tank also ensures that the depth of the wire into the water tank is fixed, so that the tensile quality of the wire is relatively stable.
⑥ The heat treatment device performs heat treatment after the wire is drawn to eliminate the internal stress generated when the wire is forced to be drawn, so as to avoid damaging the wound parts due to excessive shrinkage of the finished wire during winding; In addition, the monofilament without heat treatment will shrink in case of high temperature during application, so generally, the drawn filament needs heat treatment
There are two heating methods for heat treatment wire, which can be heated by hot air circulation or by boiling water. Generally, the temperature is lower than that of wire drawing, and the running speed of wire during heat treatment is slightly slower than that of fast drawing roller. Because the silk shrinks during heat treatment.
⑦ The winding of the finished silk of the coiling device is generally wound into coils. The reeled silk includes monofilament reeling, and some reels several strands of silk together. In order to obtain a coil with balanced tension, the coiling device is required to be driven by a torque motor.
See Table 9-2 for the specifications and parameters of domestic auxiliary production equipment for silk extrusion molding
(3) The temperature of each section of the barrel is 150~180 ℃ in the feeding section, 190~260 ℃ in the plasticizing section, and 280~310 ℃ in the homogenizing section when the monofilament extrusion raw materials are plasticized in the barrel.
The mold temperature is 290~310 ℃. The temperature of water in the cooling water tank is 30~50 ℃. The temperature of water in the stretching tank is 90~100 ℃. The drafting multiple of the silk quilt is 9~10 times (for example, if the rotational speed of the first drafting roller is 15m/min, the rotational speed of the second drafting roller should be about 150m/min).
(4) Key points of process operation
① Perforated plate and filter screen shall be added at the front end of the barrel. The filter screen shall be no less than 3 layers, and the mesh number and placement position shall be 40/80/40 mesh.
② Attention shall be paid to the accuracy of the spinneret during the work. The working surface of the spinneret hole shall be smooth and flat without residue or scratch; During disassembly, handle with care, and do not knock with a hammer to prevent deformation of the plate. See Table 9-3 for the relationship between spinneret aperture selection and finished yarn diameter.
③ The distance between the water level in the cooling water tank and the spinneret shall be controlled within 15~50mm, the water temperature shall be within 20~30 ℃, and the running length of the wire in water shall be greater than 1m.
④ The temperature during wire drawing shall be controlled below the melting point temperature of the raw material for the wire. Refer to Table 9-4 for the reference process temperature of different raw material monofilament forming.
⑤ The drawn monofilament shall be annealed to eliminate the internal stress generated during drawing and reduce the shrinkage of the filament. Hot water can be used for heat treatment and annealing of wire
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